There are two ways to delete a discount code.
From a creator's Talent Card
Go to the creator's Talent Card, click the pencil icon next to the code, and select Remove Code. This removes the code from both ShopMy and your Shopify store if you are integrated.
From the Custom Codes page
Click the menu icon in the top right of your dashboard, select Custom Codes, and click Edit next to the code you want to remove. You can also use Bulk Action to delete multiple codes at once. See How do I use bulk actions for discount codes? for steps.
If your brand is not Shopify-integrated, removing a code in ShopMy will delete it from the creator's Talent Card, but you'll also need to manually delete it in your store to ensure it's no longer active at checkout.